1. Field of the Invention
The present invention relates to an image forming apparatus for primary-transferring a toner image formed on an image bearing member onto a rotating intermediate transfer material, secondary-transferring the primary transfer image onto a recording material, and forming an image. More particularly, the invention relates to an image forming apparatus for bending the intermediate transfer material from an outer peripheral surface on which the toner image has been held to an inner peripheral surface by a bending member.
2. Description of the Related Art
In recent years, in an electrophotographic apparatus, a requirement for realization of a high picture quality, a high durability, low costs, a full color, and the like from the market has been increasing. Particularly, in recent years, the realization of a full color of documents in an office is being progressed owing to the spread of a color printer and a color copying apparatus and a requirement to realize an apparatus which outputs a full color image at a speed similar to that of a monochromatic image is increasing.
To satisfy such a requirement, an attention is paid to what is called a tandem type full color image forming apparatus. The tandem type image forming apparatus is an apparatus constructed in such a manner that a plurality of photosensitive bodies are arranged, each of the photosensitive bodies individually has a developing apparatus, a monochromatic toner image is formed onto each of the photosensitive bodies, and the monochromatic toner images are transferred and sequentially overlaid, thereby recording a synthetic color image onto a recording material.
In the tandem type image forming apparatus, a printing speed can be fairly raised and a printing time can be remarkably reduced as compared with those of what is called a one-drum type image forming apparatus which forms the synthetic full color image onto the photosensitive body by repeating the image forming operation a plurality of number of times (ordinarily, four times) by using one photosensitive body. However, since such a tandem type image forming apparatus has a plurality of image forming portions, the apparatus is liable to be enlarged in size.
The tandem type image forming apparatuses are classified into a direct transfer type and an intermediate transfer type. According to the direct transfer type, images on the photosensitive bodies are sequentially and directly transferred onto a sheet which is conveyed by a recording material conveying belt by a transfer apparatus. According to the intermediate transfer type, after the images on the photosensitive bodies are temporarily sequentially transferred onto an intermediate transfer belt by a primary transfer apparatus, the images on the intermediate transfer belt are transferred onto a recording material in a lump by a secondary transfer apparatus.
According to the intermediate transfer type, since a secondary transfer position can be relatively freely set and it is of advantage to prevention of a contamination of the photosensitive bodies because the recording material is not come into contact with the photosensitive bodies. Therefore, an attention has particularly been paid to the intermediate transfer type in recent years.
As an apparatus using such an intermediate transfer type, there has been proposed an image forming apparatus in which a bending member for pressing an intermediate transfer belt from an outer peripheral surface is provided on the downstream side of a secondary transfer position and on the upstream side of a primary transfer position in the moving direction of the intermediate transfer belt (refer to Japanese Patent Application Laid-Open No. H09-222804).
In such an image forming apparatus, the intermediate transfer belt is pressed inwardly by the bending member and a path is changed so that the belt is indented inwardly, thereby forming an empty space on the outside thereof. Since another apparatus can be arranged in such an empty space, the whole image forming apparatus can be miniaturized.
In the image forming apparatus using such a bending member, when toner leaked from both edge portions of an intermediate transfer belt cleaning member is come into contact with the belt in the pressed state between the intermediate transfer belt and the bending member, the toner is fixed to the bending member and there is a risk that the intermediate transfer belt is damaged.
On the other hand, as illustrated in FIG. 8, there has been proposed a construction in which for an intermediate transfer belt 100 which is suspended around suspending rollers 103 and is rotatable in the direction shown by arrows, an intermediate transfer belt cleaning member 101 and a bending member 102 are provided on the downstream side of a secondary transfer position and on the upstream side of a primary transfer position, and a length of bending member 102 in the width direction is set to be shorter than that of the intermediate transfer belt cleaning member 101 in the width direction (refer to Japanese Patent Application Laid-Open No. 2003-149953).
However, the above construction in which the width of bending member 102 is set to be shorter than that of the intermediate transfer belt cleaning member 101 has the following problem.
That is, since the width of bending member 102 is smaller than that of the intermediate transfer belt cleaning member 101, the width of bending member 102 is fairly shorter than that of the intermediate transfer belt 100. Thus, in edge portions of the bending member 102, such a phenomenon that the intermediate transfer belt 100 falls to the side of the bending member 102 by a tension of the intermediate transfer belt 100 occurs or wrinkles of the intermediate transfer belt 100 are liable to occur due to a concentration of stresses on the edge portions of the bending member 102.
Therefore, in the edge portions of the intermediate transfer belt cleaning member 101, the contact state of the intermediate transfer belt 100 and the intermediate transfer belt cleaning member 101 becomes unstable and a defective cleaning is liable to occur.
As a result of various studies, it has been found that the toner fouling of the edge portions of the intermediate transfer belt 100 is not always caused only by the toner leaked from both of the edge portions of the intermediate transfer belt cleaning member 101 disclosed in Japanese Patent Application Laid-Open No. 2003-149953. Rather than the leaked toner, the toner accumulated in the edge portions of the photosensitive drum is transferred onto the intermediate transfer belt 100, so that the toner fouling is accumulated.
In the image forming apparatus, a developing apparatus and a photosensitive drum cleaner are arranged around a photosensitive drum. In addition to the toner leaked from both edge portions of the photosensitive drum cleaner in the longitudinal direction, the toner scattered from the developing apparatus and the like are accumulated in both edge portions of the photosensitive drum in the longitudinal direction and a belt of the toner fouling is formed due to the durability of a long period of time. The photosensitive drum cleaner is set so as to be shorter than the photosensitive drum in order to stabilize the contact of the photosensitive drum cleaner with the photosensitive drum.
Since the toner fouling of the edge portions of the photosensitive drum is come into contact with the intermediate transfer belt 100, the belts of the toner fouling formed in the edge portions of the photosensitive drum are transferred and deposited onto the edge portions of the intermediate transfer belt 100. If the toner fouling of the edge portions of the intermediate transfer belt formed as mentioned above is come into contact with the belt in the pressed state between the intermediate transfer belt 100 and the bending member 102, the toner is fixed and deposited onto the bending member 102 as mentioned above and there is a risk that the intermediate transfer belt 100 is damaged.